Synthesis of ultrananocrystalline diamond films by microwave plasma-assisted chemical vapor deposition

Abstract

Summary form only given. Microwave plasma assisted chemical vapor deposition (MPACVD) is one of the techniques used to grow ultrananocrystalline diamond (UNCD) films in the laboratory. UNCD films are characterized as smooth films consisting of few-10's nanometer sized crystals of diamond. The exceptional properties of these films, such as high hardness and chemical inertness combined with their small crystal size and smoothness and excellent mechanical properties such as high Young's modulus, fracture toughness and low coefficient of friction, have suggested applications as a protective, hard coating material, a material/substrate for micromechanical systems and a robust conducting coating for electrochemical electrodes. The objective of this study is to deposit both thin (less than 100 nm thick) and thick (~50 micrometer thick) UNCD films of high quality across 7.5 cm diameter substrates. In this paper we report on the development of process methods to grow UNCD films using a MPACVD system. Three different gas mixtures studied include H2:Ar:CH4, N2:Ar:CH4 and H2:He:CH4. For these three plasma discharges the process for UNCD film deposition is investigated over a wide pressure range (60-180 torr) and substrate temperature range (400-8000 C). UNCD films are grown on Si (100), p-type boron doped, substrates with thicknesses ranging from 58 nm to greater than 70 mum. The effect of various inputs such as feed gas mixture, pressure, substrate temperature and nucleation methods on growth rate, surface morphology, uniformity, and conductivity of UNCD diamond films is investigated. The highest growth rate of 1.12 mum/h was achieved at 180 torr, with gas mixtures of H2:Ar:CH4 = 4:100:2 seem and 3 kW microwave power. Film surface roughness, as low as 10 nm, was obtained as measured by AFM microscope